Games Workshop proportions are horribly out of true which is why so many truescale models looks weird, they exaggerate the already deformed Games Workshop models and highlight the problems they have.
The scale of the models is all over the shop with the Death Cultist models being some of the more accurate Games Workshop models, and compare them to a regular figure and they are tiny. At 28mm scale, your average human should stand 28mm high (some do take this to the eye level only but it is better to have it to head height and you see this with many 32mm scale miniatures (which, whilst much taller than a Games Workshop figure have far thinner limbs, and bodies, smaller heads et cetera) and this would represent an average 5'9" human. If we were to say a Space Marine was 7' precisely that would require a model 34mm tall.
If you were to make a scale miniature of an 8' Space Marine, a not unreasonable size based on the background, then the model would be 38mm tall, considerably bigger than your average human character.
Mostly you will find that human and Space Marine models are 30mm tall. Eldar models suffer by being too short, Tau too tall and only orks, who stand about 6' are accurately portrayed.
You can see the problem with human figures with this image:
This is an unarmoured and armoured Space Marine I made a long while ago at 54mm scale. You can see how the Marine looks (a smidge under 7' tall the model is 66mm where Artemis is, according to Jes Goodwin, supposedly 67mm tall, downscaled from a 7' 6" drawing) next to a regular human and then how Games Workshop's heroically scaled 54mm Marine looks in comparison.
I don't say my own models are perfect by any stretch but they are fairly accurate scale figures, not heroic, and I think they do serve to show how Games Workshop figures differ enormously from what would be an accurate scale miniature. But then they don't make scale miniatures they make wargames models and making a space marine bigger is a lot easier than making a guardsman smaller.